Department of Biochemistry and Genetics, The Connecticut Agricultural Experiment Station, P.O. Box 1106, New Haven, Connecticut 06504.
Plant Physiol. 1986 Feb;80(2):473-8. doi: 10.1104/pp.80.2.473.
Serine:glyoxylate and glutamate:glyoxylate aminotransferases (SGAT and GGAT), which catalyze the formation of glycine from glyoxylate during photorespiration, have been purified >300-fold from tobacco leaf extracts. Incubation with glyoxylate in the absence of amino acid substrate resulted in the time- and concentration-dependent inhibition of the partially purified enzymes. The second order rate constants for glyoxylate inhibition were 1.25 and 0.175 per millimolar per minute for SGAT and GGAT, respectively. The enzymes of highest specific activity were not inhibited by 5 millimolar glyoxylate alone but when 1 millimolar NH(4) (+) was added to 1 millimolar glyoxylate for 10 min in the absence of amino donor, SGAT was irreversibly inhibited more than 50%. GGAT was inhibited 50% in 10 minutes by 15 millimolar NH(4) (+) and 1 millimolar glyoxylate. By itself, NH(4) (+) was a reversible inhibitor; SGAT and GGAT were inhibited 50% at 6 millimolar and 50 millimolar, respectively. The irreversible inhibition occurred only with glyoxylate and NH(4) (+) added together; oxalate, formate, acetaldehyde, pyruvate, hydroxypyruvate, and alpha-ketoglutarate did not inhibit either in the presence or absence of NH(4) (+). Glyoxylate and NH(4) (+) could form a carbinolamine which is a serine analog and might bind irreversibly to the enzymes. Under conditions in vivo in which reassimilation of NH(4) (+) is reduced or blocked, the activity of SGAT may be inhibited and if glyoxylate is available, as in leaf peroxisomes, irreversible inhibition may occur.
乙醛酸和谷氨酸：乙醛酸氨基转移酶（SGAT 和 GGAT），能催化光呼吸过程中乙醛酸与甘氨酸的形成，已从烟草叶提取物中被纯化 300 多倍。在无氨基酸底物的情况下孵育乙醛酸会导致部分纯化的酶出现时间和浓度依赖性抑制。SGAT 和 GGAT 的乙醛酸抑制的二级速率常数分别为每分钟每毫摩尔 1.25 和 0.175。具有最高比活的酶不受 5 毫摩尔乙醛酸单独抑制，但当 1 毫摩尔 NH₄⁺在 10 分钟内添加到 1 毫摩尔乙醛酸中而无氨基供体时，SGAT 不可逆地被抑制超过 50%。在 10 分钟内，15 毫摩尔 NH₄⁺和 1 毫摩尔乙醛酸可使 GGAT 抑制 50%。自身而言，NH₄⁺是可逆抑制剂；SGAT 和 GGAT 分别在 6 毫摩尔和 50 毫摩尔时被抑制 50%。只有当乙醛酸和 NH₄⁺一起添加时才会发生不可逆抑制；草酸盐、甲酸盐、乙醛、丙酮酸盐、羟基丙酮酸和α-酮戊二酸在有或没有 NH₄⁺的情况下均不抑制。乙醛酸和 NH₄⁺可以形成一种羟胺，它是丝氨酸的类似物，可能会不可逆地与酶结合。在体内重新同化 NH₄⁺减少或受阻的条件下，SGAT 的活性可能受到抑制，如果有乙醛酸存在，如在叶过氧化物酶体中，则可能发生不可逆抑制。
